One of the most important concepts to emerge in recent years in opiate research is the concept of multiple opiate receptors. Originally proposed as "Receptor Dualism", this concept has now been expanded to a whole variety of pharmacologically-defined receptor classes, including mu, delta, kappa, sigman and epsilon. Most recently, two subtypes of mu receptors have been proposed. One, the mu2 site, corresponds to the morphine-selective mu receptor previously characterized. The other, the mu1 site, represents a site first recognized in homogenate binding studies which binds both opiates and opioid peptides with similar very high affinities. The selective mu1 antagonists naloxonazine and naloxazone have proven very helpful in defining the pharmacological role of mu1 sites, implicating them in supraspinal analgesia, for example, but not in respiratory depression or most signs of physical dependence. This application proposes three major aims. The first consists of the characterization of the various classes of opiate binding sites. It consists of the development of selective binding assays for mu1, mu2, delta and kappa sites, followed by their biochemical and pharmacological characterization. The second aim involves the localization of these binding sites using digital subtraction computerized autoradiography. These studies will attempt to localize mu1, mu2, delta and kappa sites using a sophisticated computer analysis to regions within the brain as well as their pre- versus post-synaptic distributions. The last major aim involves continuation of studies on the characterization of a number of irreversible opiates. These compounds will be characterized in binding studies and their selectivity correlated with their pharmacological actions. Selected compounds will be utilized as affinity labels for the receptor. Ultimately, studies such as these should lead to the development to a better understanding of the actions of opiates and their more effective use in the management of pain.